Question

I know that there is Jerkson and scalaxb and even Java’s XStream that successfully able to serialize scala’s data. I know that they handle well Strings, Integers and even case classes pretty well. But if I have function as one of the fields?

e.g. if I have something like:

case class Foo(bar: (Int) => Boolean, baz: Int) 

Can these fields been somehow serialized to JSON or XML (actually, I don’t care to which one, they should be human-readable, thats why I don’t want to use SBinary)?

EDIT

Why would I want to do that?
Right now I’m writing implementation of decision tree. I don’t want to reconstruct that trees every time from training data hence I need to serialize them and that part could be done with SBinary. But additionally, it would be nice if as a humans we could look at serialized tree and analyze it.

It is not so wide task as I wrote in title, yes.
What I thinking now, is to write a custom serializer (e.g. for Jerkson) with my own format, or write to string field and then parse this back.

But I though that there could be some insanely better way to perform that.

Answer 1

No, a function is not necessary serializable… and serializable functions are unlikely to provide a human readable serialization.

If you want to be able to provide any kind of function, Im’ afraid there won’t be any solution. A possible workaround, if it can be used in your scenario, is to build a case class that implements Function[Int, Boolean] and thus to go back to a case class scenario.

For example, suppose that you have isolated that all your functions check whether a integer is exactly divisible by a given integer:

case class Mod(mod: Int) extends Function[Int, Boolean] { //the extends part is not even require
  def apply(x: Int) = x % mod == 0
}

case class Foo(bar: Mod, baz: Int)

It’s clearly ultra-restrictive. But I’m afraid it’s the best you can achieve.

According to your edit. A solution might be to have a kind of factory class:

case class IntTest(humanReadableDescription: String) {
  def apply(x: Int) = IntTest.fromString(humanReadableDescription)(x)
}

object IntTest {
  private val fromString = Map[String, Function[Int, Boolean]] (
     "mod2" -> {x:Int => x % 2 == 0},
     "is42" -> {x:Int => x == 42}
  )
}

case class Foo(bar: IntTest, baz: Int)

But here, you will lose type safety.